Objectives: In thyroid textbooks it is stated that hyperthyroidism in women may be associated in almost 50% of the cases with hypomenorrhoea, oligomenorrhoea or amenorrhoea and perhaps with reduced fertility. Our experience at a busy thyroid clinic has given a picture which differs from that described in the literature. Most of our female thyrotoxic patients had normal menstruation. This study was performed to define the menstrual abnormalities in hyperthyroidism.
Design and patients: We investigated the menstrual history, starting 6 months before the discovery of the disease, the smoking habits and the body mass index (BMI), in 214 female, premenopausal thyrotoxic patients and a similar number of normal controls matched for age and weight.
Measurements: TT4 and TT3 were measured by radioimmunoassay, while BMI was calculated from the ratio of body weight in kg to height in m2.
Results: Of the 214 patients, 168 (78.5%) had regular menstrual cycles and 46 (21.5%) irregular cycles. No difference in BMI was found between the patients with or without menstrual abnormalities. Out of the 46 patients with irregular periods, 23 (50%) were smokers, while only 32 out of the 168 patients (19%) with normal periods were smokers (P < 0.001). TT4 levels were higher as a group in patients with menstrual disturbances (mean +/- SD 267.7 +/- 66.9 nmol/l) than in those with normal periods (240.6 +/- 47.6 nmol/l) (P < 0.05). The 23 smokers with irregular periods had higher TT4 levels (280.5 +/- 51.8 nmol/l) than the remaining non-smokers from the same group (241.9 +/- 43.7 nmol/l) (P < 0.01). No such differences were found for TT3 levels. Out of 214 normal controls, matched for age and weight, 196 (91.6%) had normal menstruation and 18 (8.4%) irregular cycles. The latter group included mainly women with oligomenorrhoea. Out of 18 normal controls with irregular periods, 6 (33.3%) were smokers, while 57 (29.1%) out of 196 with normal periods were smokers.
Conclusions: These data demonstrate that hyperthyroidism in women is less frequently associated with menstrual abnormalities than was previously believed. Furthermore, no patient presented with amenorrhoea. Smoking and TT4 levels are strongly associated with the occurrence of menstrual disturbances in thyrotoxicosis.